The present invention relates to an improvement in a process for preparing a tinted contact lens. In particular, the invention relates to a process for proving a solid, unblemished layer of coloring agent onto the surface of an unhydrated hydrophillic contact lens.
There are many known methods for tinting or otherwise coloring contact lenses. For example, a coloring agent, such as a dyestuff or pigment, may be dispersed in a monomer precursor or polymer matrix. This method is typically unsuitable for use in hydrophilic contact lenses, however, because the coloring agent leaches from the polymer upon the presence of water in the lens. Also, this method does not provide the ability to color the polymer once it has been made into a lens.
Another known method of coloring lenses is printing or otherwise applying the coloring agent to the lens surface. This method has been performed using standard transfer print devices, such as a TAMPO RAPID 2000/3 pad printing machine from Transtech America Inc., Chicago, Ill. Typically, the printing method employs solvent-based coloring agent applied to the lens with a silicone rubber pad. This method is also problematic in that it does not provide an unblemished, solid covering of colorant on the dry lens surface. One attempt at solving this problem has been known to create a solid pattern from a plurality of overlying halftone dots using multiple transfer printing steps. This process is not totally satisfactory, however, in that the resulting colorant cover is blemished or mottled. Another proposed solution to the problem associated with transfer printing of colorant to a hydrophilic surface has been to abandon using solid colorant coverings altogether, and replacing it with known halftone patterns on dry lens having spaces. However, surface tinting remains the preferred method of applying color to contact lenses.
There exists a need, therefore, for a process of providing a solid, unblemished colorant onto an unhydrated contact lens made of hydrophilic material.
There exists a further need for such a method as described above which utilizes standard transfer printing technology, particularly that involving "off-the-shelf" silicon rubber printing pads.
There exists a still further need for such a process which incorporates a single printing step.